The presently disclosed subject matter relates to a sensor and a biological signal measuring system.
A blood refill time is one of indexes for observing a tissue perfusion of a subject. The blood refill time is used as a simple index for evaluating whether shock has occurred. The blood refill time is widely used in the field of emergency medicine for the purpose of determining necessity of transfusion, triage (evaluation of priority in a case where many persons are injured or sickened) or the like.
Generally, when measuring a blood refill time, a medical person applies pressure on a living tissue of a subject, such as a finger nail, and after the pressure is released, visually checks the color change of the nail or the skin. When the color returns to an original color within approximately two seconds, it is determined that the subject is in a normal condition. In this technique, however, because the living tissue is manually pressed and the change of the skin color is visually checked, it cannot provide quantitative results and an error easily occurs.
A related art blood refill time measurement uses a pulse oximeter (see, e.g., US2007/0282182A1). More specifically, light of a wavelength which can be absorbed by blood enters living tissue, and the intensity of light which transmits through the living tissue is measured by an optical sensor. In this case, when the living tissue is pressed by using an actuator, blood is evacuated from the living tissue of the pressed portion, and hence the intensity of the transmitted light is increased. When the pressure is released, the living tissue of the portion is filled with blood, and therefore the intensity of the transmitted light is decreased. The blood refill time is identified based on the time elapsed from the release of the pressure until the transmitted light intensity returns to the original level.
In order to perform a reproducible and quantitative measurement of the blood refill time, it is necessary to provide the same condition of applying pressure on living tissue. In the configuration where the living tissue is directly pressed by an actuator, however, it is difficult to always bring the actuator to contact the same portion of the living tissue. When the contacting position changes, the condition of applying pressure also changes, and therefore the reproducibility of measurement results is lowered.
The living tissue may compressed by using an air bag or the like. Depending on the material of the air bag, however, the light entering the living tissue, and the transmitted light (or reflected light) from the living tissue are affected, and the accuracy of measurement results may be lowered.